There are known cryogenic surgical instruments comprising a device connecting a working member and a source of ultrasonic vibrations, a jacket for refrigerant circulation, which is disposed between the base of the instrument and the ultrasonic source, and a calibrated prefice in the inlet for the refrigerant (Su, A, 460 869). This instrument is deficient in that it cannot be used for surgical operations because it cannot dissect tissues.
Known in the art is a cryogenic ultrasonic scalpel comprising a housing accomodating a source of ultrasonic vibrations, a blade connected to this ultrasonic source via a transformer, and a tubular heat exchanger for supplying and bleeding the refrigerant to and from the blade. The heat exchanger is a U-shaped tube installed in thermal contact with a lateral surface of the blade and connected to refrigerant inlet and outlet pipes by bellows located in the standing wave zone formed zone at the junction of the blade with the ultrasonic source, the tubes of the heat exchanger being made narrowing in the direction of the cutting edge of the scalpel (SU, A, 825 056).
This cryogenic ultrasonic scalpel is deficient in that the speed of dissection of soft and parenchymal tissues is inadequately low and the hemostatic effect is insufficient.
A low dissection speed is due to the fact that in prior art cryogenic ultrasonic scalpels the cutting device has a negative temperature when in operation. This means that when tissue is dissected the cutting action of the scalpel is only due to the ultrasonic effect and the expected cutting action of dissecting a hard layer of tissue froze by the previous dissection is not realized. The dissection speed is low also because the refrigerating capacity is insufficient and the blade is cooled unsymmetrically, since refrigeration is from the U-shaped heat exchanger whereby the lateral surface of the blade, which is closer to the inlet, is cooled more than the other lateral surface thereof, the temperature of the refrigerant in the outlet being higher. This may cause sticking of tissue to the cutting tool and the heat exchanger. In addition, the scalpel blade has a thermal contact with the ultrasonic transformer which is a powerful heat source and this only adds to the unsymmetrical cooling of the blade. The heat from this ultrasonic transformer also contributes to raising the temperature of the scalpel blade and is, therefore, the reason of refrigeration shortage during tissue dissection. The speed of tissue dissection becomes still slower and the hemostatic effect is decreased, which prolongs the operation period quite substantially.
Moreover, the U-shaped heat exchanger wherein refrigerant inlets and outlets are set wide apart makes the instrument bulky and inconvenient.
In addition, prior art cryogenic ultrasonic scalpels have no capability to control the level of ultrasonic and low-temperature effects on the dissected tissue, which makes the instrument less efficient. Since the level of the low-temperature action cannot be monitored, the hemostatic effect may be insufficient during an operation or become the cause of post-operational necrosis of tissues in the organ being operated.
The absence of means for monitoring the level of ultrasonic action is the cause of injury to the organ being operated, e.g. by too a high temperature of the dissected tissue added to the intensive ultrasonic action.